Developing: Tucson Airbase On Lockdown

The Davis-Monthan Air Force base in Tucson, Ariz. is on lockdown. The AP, as well as local news outlets, report the Air Force base has confirmed that it has stepped up security, but it refused to give details of the situation.

The AP reports:

Senior Airman Timothy Dunaway says traffic has been reduced to a single point entry but he refused to elaborate.

He says the Sonoran Science Academy on the base is on lockdown.

The Arizona Daily Star reported that gunshots had been fired, but the AP reports the spokesman could not confirm the report. The paper also reported about "seven rescue units were seen racing into the base just before noon."

The base is best known as the boneyard for old military and government airplanes.

The Pima Air & Space Museum south of the base remains open, but public tours that it does on the base have been canceled, officials said.

This is a developing news story. We'll update as we get more, so make sure you refresh this post.

Update at 3:39 p.m. ET. No Shots Fired:

From the AP: Davis-Monthan Air Force Base spokeswoman says no shots have been fired at Tucson air base.

Update at 4:23 p.m. ET. Reports Of Gunman Not Confirmed:

The lockdown at facility was prompted by reports of someone with "something that looked like a weapon," Tech Sg. Russ Martin told AP. However, the reports have not been confirmed.

The ambulances seen on the base were just a bad coincidence an official told the AP.

Update at 5:56 p.m. ET. Lockdown Continues:

The lockdown continues on the base and details are still scarce. KVOA is reporting that a SWAT team and a bomb squad are on the scene, while The Arizona Republic reports that an armed civilian "got on to the base and barricaded himself in a room on the second floor of a building known as the 'Old Dorm,' a source told The Arizona Republic."

The paper adds that the man took no hostages and that authorities were negotiating with him.

Copyright 2011 National Public Radio. To see more, visit http://www.npr.org/.